The transfer of fluids to a moving web surface is well known in the art. The selective transfer of fluids for purposes such as printing is also well known. The selective transfer of a fluid to a surface by way of a permeable element is well known. Screen printing is a well known example of the transfer of a fluid to a surface through a permeable element. The design transferred in screen printing is formed by selectively occluding openings in the screen that are located according to the formation of the screen. The aspect ratio of the holes and fluid viscosity may limit the fluid types, application rate, or fluid dose that may be applied with screen printing.
Gravure printing is also a well known method of transferring fluid to the surface of a moving web material. The use of fixed volume cells engraved onto a print cylinder ensures high quality and consistency of fluid transfer over long run times. However, a given cylinder is limited in the range of flowrates possible per unit area of web surface.
Previous fluid application efforts have also utilized sintered metal surfaces as transfer elements. A pattern of permeability has been formed using the pores in the element. These pores may be generally closed by plating the material and then selectively reopened by machining a desired pattern upon the material and subsequently chemically etching the machined portions of the element to reveal the existing pores. In this manner a pattern of permeability corresponding to the pores initially formed in the material may be formed and used to selectively transfer fluid. The nature of the pores in a sintered material is generally such that the tortuosity of the pores predisposes the pores to clogging by fluid impurities.
The placement of the fluid is limited in the prior art to the pores or openings present in the material that may be selectively closed or generally closed and selectively reopened. The present invention provides an ability to form a pattern of permeability by forming pores at selected locations. The location of the fluid transfer points may be decoupled from the inherent structure of the transfer medium.
The present invention also provides for a broad range of fluid flow per unit area of the web surface by manipulating the motive force on the fluid across the fluid transfer points.